1. Field of the Invention
This invention relates to bulk single crystal binary, ternary or quaternary metal nitrides such as gallium nitride, such metal nitrides being referred to broadly hereafter by the symbol M*N, including single crystal M*N substrate articles useful for formation of microelectronic structures thereon, as well as to an appertaining method of forming M*N in single crystal bulk form.
2. Description of the Related Art
The III-V nitrides, in consequence of their electronic and optical properties and heterostructure character, are highly advantageous in the fabrication of a wide range of microelectronic structures. In addition to their wide band gaps, the III-V nitrides also have direct band gaps and are able to form alloys which permit fabrication of well lattice-matched heterostructures. Consequently, devices made from the III-V nitrides can operate at high temperatures, with high power capabilities, and can efficiently emit light in the blue and ultraviolet regions of the electromagnetic spectrum. Devices fabricated from III-V nitrides have applications in full color displays, super-luminescent light-emitting diodes (LEDs), high density optical storage systems, excitation sources for spectroscopic analysis applications, etc. High temperature applications are found in automotive and aeronautical electronics.
To effectively utilize the aforementioned advantages of the III-V nitrides, however, requires that such materials have device quality and a structure accommodating abrupt heterostructure interfaces, viz., III-V nitrides must be of single crystal character, substantially free of defects that are electrically or optically active.
A particularly advantageous III-V nitride is GaN. This nitride species can be utilized in combination with aluminum nitride (AlN) to provide optically efficient, high temperature, wide band gap heterostructure semiconductor systems having a convenient, closely matched heterostructure character similar to that of GaAs/AlAs. Indium nitride may also be added to GaN or AlN to provide additional advantages.
Corresponding advantages are inherent in ternary GaN compositions of the shorthand formula MGaN, wherein M is a metal compatible with Ga and N in the composition MGaN, and the composition MGaN is stable at standard temperature and pressure (25° C. and 1 atmosphere pressure) conditions. Examples of potential M species include Al and In. Such compounds have compositions described by the formula M1-xGaxN, where x ranges from 0 to 1. The addition of a third compatible metal provides quaternary alloys of general formula M1-x-yM′yGaxN, where M and M′ are compatible metals, in particular Al and In, and x and y range from 0 to 1. Such quaternary alloys are referred to by shorthand formula AlGaInN.
Alloys of GaN, AlN or InN with silicon carbide (SiC) may be advantageous because they can provide modulated band gaps. Such alloys have in the past been difficult to grow in single crystal form.
For ease of reference in the ensuing disclosure, therefore, the term “M*N” is defined as including binary (e.g., GaN), ternary (MGaN), and quaternary (MM′GaN) type gallium nitride type compounds, as well as SiC, SiC/AlN alloys, SiC/GaN alloys, SiCInN alloys, and other related compounds such as alloys of SiC with AlGaN. All possible crystal forms are meant to be included in this shorthand term, including all cubic, hexagonal and rhombohedral modifications and all SiC polytypes. Examples of these compounds include AlN, InN, AlInN, AlGaN, InGaN, and AlInGaN.
For device applications, therefore, it would be highly advantageous to provide substrates of M*N, for epitaxial growth thereon of any of the M*N materials, especially GaN, AlGaN, InGaN, or SiC, for the production of heteroepitaxial devices. Unfortunately, however, it heretofore has not been possible to produce GaN in single crystal bulk form, and for all M*N materials, growth of high quality bulk single crystals has been fraught with difficulty.
It therefore would be a significant advance in the microelectronics art, and is correspondingly an object of the present invention, to provide M*N in bulk single crystal form, suitable for use thereof as a substrate body for the fabrication of microelectronic structures.
It is another object of the present invention to provide an appertaining method for the formation of bulk single crystal M*N which is relatively simple and may be readily achieved using conventional crystal growth techniques in an economic manner.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.